Multi-component surfaces are of enormous importance with applications in electronics, photonics, genome analysis, drug discovery, and cellular systems. Surfaces designed with a precise arrangement of conductive or insulating materials form the basis of modern Electronic devices. Chemically heterogeneous surfaces have been fabricated for use in biochemical sensing (Fodor et al. Nature 1993 364:555) and in assembling arrays of living cells (Graighead et al. Curro Opin. Solid State Mat. Sci. 2001 5:177). In general, previous strategies for fabricating such devices have relied on highly planar surfaces formed from brittle crystalline materials, such as silicon or gallium arsenide. These fabrication strategies often employ high temperatures, pressure, chemical solvents and other harsh conditions, which cannot be used on more delicate materials. Today, there is an emerging paradigm of microdevices based on surfaces that are highly curved or flexible, and on materials that are soft or delicate, such as organic molecules and other polymers. There is a need for new patterning strategies that can handle these materials and surfaces. Several groups have attempted to fabricate these surfaces by direct writing methods using converted scanning probe microscopes (Demers et al. Science 2002 295:1701; Cao et al. Science 2002 296:1838; and Bruckbauer et al. JACS 2003 125:9834); however these methods are only useful for patterning small areas. Other techniques have been based on self-assembly (or bottom-up assembly). Self-assembly techniques are massively parallel; however, most traditional self-assembly techniques fall short when it comes to assembling more than one type of component. Accordingly, building multi-component surfaces on a commercial scale at the nanoscale and microscale level has remained a major challenge because of the high precision and parallelism that is simultaneously required to create such surfaces. While significant time and resources have been invested in the area of multi-component nanopatterning, no single technique has been developed to date that is capable of satisfying both requirements of resolution and speed.
Fabrication of heterogeneous substrates of the kind used for combinatorial chemistry, drug discovery and genomics typically requires multiple lithographic steps. For example, heterogeneous substrates have been successfully fabricated by photolithography (McGall et al. JACS 1997 119:5081). However, photolithography is an expensive, chemically intensive, and laborious process typically requiring multiple steps to produce even a single pattern. These steps include optical masking to selectively expose and develop areas of photoresist material, followed by etching or depositing material through the photoresist masking pattern, and finally dissolving the photoresist mask. Creating heterogeneous substrates by photolithography requires repeating the alignment and registration steps for each new pattern in order to ensure proper geometric relation between the patterns on the surface. Manual alignment and registration of many different masks to the substrate becomes increasingly difficult to control when the critical feature size is micron or even sub-micron in resolution or when the number of aligned patterns becomes very large. It is in these cases particularly, where the ability to self-align the masking material onto the surface is expected to be useful.
Programmable assembly of micron-sized colloidal particles, carrying various molecules, such as proteins, DNA fragments or fluorescent labels, into precise geometric patterns has been demonstrated using magnetic forces and magnetically encoded surfaces (Yellen et al. J. Appl. Phys. 2003 93:7331). Previous work has shown that the number of particles deposited (or not deposited) at each surface site can be reliably controlled through a combination of magnetic and morphological template features. Regular heterogeneous colloidal patterns were assembled by this technique using only physical forces (i.e. magnetic, hydrodynamic and surface forces). The theoretical process of particle assembly onto magnetic surfaces has also been analyzed in order to guide experimental investigations (Yellen et al. 2002 J. Appl. Phys. 912:855; Yellen et al. J. Appl. Phys. 2003 93:8447; Plaks et al. IEEE Trans. Mag. 2003 39:1436; and Hovorka et al. IEEE Trans Mag. 2003 39:2549).
In the present invention, a method is provided for depositing magnetic nanoparticles at programmed locations on a substrate surface in order to mask selected sites rather than to deliver molecules using magnetic particles as the carriers. In this method, the magnetic nanoparticles are programmed to accumulate at selected sites on the substrate in order to mask these selected sites from, for example ultraviolet radiation and/or chemically reactive molecules or binding of a molecule such as a protein or a nucleic acid.